WO2003068867A1

WO2003068867A1 - Composition for ink jet printing comprising two or more azo dyes

Info

Publication number: WO2003068867A1
Application number: PCT/GB2003/000532
Authority: WO
Inventors: Janette Cordwell; Maria Soteri Hadjisoteriou
Original assignee: Avecia Limited
Priority date: 2002-02-15
Filing date: 2003-02-07
Publication date: 2003-08-21
Also published as: GB0203616D0; AU2003245688A1

Abstract

A composition comprising a black dye such as Luganil TM Black NT or salts thereof and a magenta dye of specified formula or salts thereof. Also claimed are inks containing this composition, an ink jet printing process using the inks, a substrate printed with the inks, an ink jet printer cartridge containing the inks and an ink jet printer containing the ink jet printer cartridge.

Description

COMPOSITION FOR INK JET PRINTING COMPRISING TWO OR MORE AZO DYES

This invention relates to a composition comprising two or more dyes, to inks containing such compositions and to processes using said inks in printing and imaging technologies, especially ink jet printing, and to printed substrates and to ink-jet printer cartridges. Ink jet printing is a non-impact printing technique which involves ejecting, thermally or by action of an oscillating piezo crystal, droplets of ink continuously or on demand from a fine nozzle directly onto a substrate but without contacting the substrate.

The inks used in an ink jet printer are required to meet a number of criteria. In the black shade area it is desirable to obtain prints with neutral black shades with good fastness properties but this has been difficult to achieve. In addition the inks desirably provide sharp, non-feathered images which have good waterfastness, gas fastness, lightfastness and optical density. The inks are required to dry quickly when applied to a substrate, however, they must not dry or crust over in the ink jet head as this can result in clogging of the ink jet nozzle. The inks are also required to be storage stable for long periods of time without deterioration in the properties of the ink.

C.I. Acid Black 210 is a known dye for ink jet printing inks. However, this dye suffers from poor shade and fading characteristics.

Inks containing mixtures of certain C.I. Direct Black dyes with certain other dyes are known for ink jet printing (JP 62-000567). Now we have found that mixtures of certain dyes are valuable as colorants for ink jet printing inks providing neutral black shades with good fastness properties.

According to a first aspect of the present invention there is provided a composition comprising a black dye of Formula (1 ) or salt thereof and a magenta dye of Formula (2) or salt thereof:

Formula (1) wherein: A and B are optionally substituted aryl groups, substituents on A being selected from NO₂ CN, SO₃H, CO₂H and substituents on B being selected from NR^aR^b where R^a and R^b are each independently selected from H or optionally substituted C_1-6 alkyl; m is 0 or 1 ; n is 0 or 1 ; such that m + n is not less than 1 ;

Z is:

R¹ and R² are each independently chosen from H or optionally substituted alkyl, optionally substituted alkoxy, SO₃H or CO₂H; L is chosen from NH, SO₂NH and CONH;

Ar¹-N=N-J-X-G-X-J-N=N-Ar²

Formula (2)

wherein:

Ar¹ and Ar² are each independently aryl each of which carries at least two carboxy groups; each J is independently:

is a group of the Formula (3a) or (3b):

Formula (3) in which T¹ and T² are each independently H, C_1-4-alkyl, C^-alkoxy or C₃.₄-alkenyl; and T³ and T⁴ are each independently H, C_M-alkyl, C_1-4-alkoxy or C₃.₄-alkenyl provided that T³ and T⁴ are not both H; each X independently is a group of the Formula (4), (5) or (6):

Formulae (4) - (6)

each Q independently is H, halogen, alkyl, NR³R⁴, SR⁵ or OR⁵; each Y independently is Z, SR⁶ or OR⁶; each E independently is Cl or CN; and

R³, R⁴, R⁵ and R⁶ are each independently H, alkyl, substituted alkyl, alkenyl, substituted alkenyl, cycloalkyl, aryl, substituted aryl, aralkyl, substituted aralkyl or R³ and R⁴ together with the nitrogen atom to which they are attached form a 5 or 6 membered ring.

Substituents on A are each preferably NO₂, CO₂H or SO₃H, most preferably NO₂.

Substituents on B are preferably NR^aR^b as hereinbefore defined, more preferably where at least one of R^a and R^b is H and the other is C_1-6-alkyl, most preferably where both R^a and R^b are H. In Z, R¹ and R² are preferably independently chosen from H, CO₂H or SO₃H, most preferably R¹ and R² are both H. L is preferably SO₂NH.

It is preferred that the dye of Formula (2) has at least as many carboxy groups as sulpho groups.

Each of the groups Ar¹ and Ar² is preferably naphthyl or phenyl carrying at least two carboxy groups, especially phenyl which may carry further substituents in addition to the two carboxy groups. The additional substituents are preferably selected from alkyl, especially C_1-4-alkyl; alkoxy, especially C_1-4-alkoxy; -SO₃H; -PO₃H₂; -COSH; -OH; -CO₂H; halogen, especially Cl or Br; and optionally substituted C_1-4-alkyl. However, it is preferred that each of Ar¹ and Ar² carries two carboxy groups and is free from further substituents, and is more preferably dicarboxyphenyl, e.g.2,4-dicarboxyphenyl, 2,3- dicarboxy-phenyl, 3,4-dicarboxyphenyl, and especially 3,5-dicarboxyphenyl. It is also preferred that Ar¹ and Ar² are identical.

It is preferred that the chromophores comprising Ar¹N=N-J- and Ar²N=N-J- are identical or similar so that they absorb light at approximately the same wavelength.

The variable -SO₃H group in each J, which may be meta- or para- with respect to the NH group, is preferably in the meta-position, so that J is the divalent residue of H- acid.

Examples of the C_1-4-alkyl, C_1-4-alkoxy and C^-alkenyl groups represented by T¹,

T², T³ and T⁴ in the divalent group G are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, t-butyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy, t-butoxy and allyl. In the group of Formula (3a), T¹ and T² are preferably identical, more preferably C_1-4-alkyl and, especially, each is methyl, so that L is especially 2,5- dimethylphen-1 ,4-ylene-diamino. In the group of Formula (3b), T³ is preferably H or C_1-4- alkyl, especially methyl and T⁴ is preferably H or C_M-alkyl, especially methyl provided T³ and T⁴ are not both H, and L is especially preferably 2,5-dimethylpiperazin-1 ,4-ylene or 2- (5-)methylpiperazin-1 ,4-ylene. When X is of Formula (5) it is preferred that Q is attached to the carbon atom between the two ring nitrogen atoms and that Y is para to Q. Each X is preferably of Formula (4).

Q is preferably Cl, OR⁵, SR⁵ or NR³R\ especially Cl; OH; SH; alkoxy, such as methoxy or ethoxy; hydroxy-C₂.₄-alkylamino, such as mono or di-(2-hydroxyethyl)amino; morpholinyl; piperidinyl; piperazinyl; 4-(hydroxy-C_2-4-alkyl)-piperazin-1-yl, such as

4-hydroxyethylpiperazin-1-yl; 4-(C_1-4-alkyl)piperazin-1-yl, such as 4-methylpiperazin-1-yl; C e-alkylamino, such as dimethylamino, n-butylamino or n-hexylamino; carboxy-C-_1-4- alkylamino, such as 2-carboxymethylamino; arylamino, such as phenylamino, mono-3- or di-3,5-carboxyanilino; or aralkylamino, such as benzylamino, mono-3- or di-3,5- carboxyphenylmethylamino. Where Q is alkyl or alkoxy these preferably contain from

1 to 4 carbon atoms. Where at least one Q is halogen, the compound of Formula (2) may be reactive with cellulose under appropriate temperature and pH conditions. However, this does not appear to contribute to the wet-fastness of the compound when applied to a paper substrate under the normal conditions used in ink jet printing and compounds in which Q is not a cellulose reactive group have been found to give equally wet-fast prints on paper to those in which Q is a cellulose reactive group.

Each of R , R , R⁵ and R independently is preferably selected from H; C_π. 10 alkyl.especially C_1-4-alkyl; substituted C_1-10-alkyl, especially substituted C_M-alkyl; phenyl; substituted phenyl; (CH₂)_1-4-phenyl; and substituted (CH₂)_1-4-phenyl, especially benzyl and substituted benzyl. When any one of R^a, R^b, R\ R², R³, R⁴, R⁵ or R⁶ is substituted, the substituent is preferably selected from -OH, -CH₃, -OCH₃, -SO₃H and -CO₂H. When R³ and R⁴ together with the nitrogen radical to which they are attached form a 5- or 6- membered ring, this is preferably morpholine, piperidine or piperazine especially the latter in which the free ring N-atom may be, and preferably is, substituted by a C_1-4-alkyl or hydroxy-C₂^-alkyl group.

The present invention relates not only to mixtures of compounds of Formula (1) and Formula (2) in the free acid form, but also to a salt or salts thereof, especially an alkali metal, ammonium or substituted ammonium salt. Alkali metal salts are preferably sodium, lithium or potassium. Although Formulae (4), (5) and (6) are represented in neutral form, the present invention also covers quaternised forms thereof, particularly where the compound of Formula (2) is in zwitterionic form.

In preferred compositions of the present invention, the compound of Formula (2) is one in which Ar¹ and Ar² are both 3,5-dicarboxy phenyl, in the form of mono-, di- or trialkylammonium salts where the alkyl is preferably C_1-4 alkyl, most preferably ammonium, methylammonium or dimethylammonium; in each J the sulpho groups are in the 3,6-positions; each X is of Formula (4) in which Q is Cl, NR³R⁴ or OR⁵ and L is 2,5- dimethylphen-1 ,4-ylenediamino, 2-methylpiperazin-1 ,4-ylene or 2,5-dimethylpiperazin- 1 ,4-ylene. In such a compound of Formula (2) it is especially preferred that Q is halogen, especially Cl; OH; C_1-4-alkoxy, especially methoxy; hydroxy-C^-alkylamino, especially 2-hydroxyethylamino; morpholin-1-yl; piperidin-1-yl, piperazin-1-yl, -(C_1-4-alkyl)piperazin- 1-yl and 4-(hydroxy-C_2-4-alkyl)-piperazin-1-yl.

An especially preferred dye of the Formula (1) is of the Formula (7) below or a salt thereof:

The above dye is available commercially as Luganil™ Black NT.

The composition may contain a single dye of Formula (2) or a mixture of two or more different dyes of Formula (2).

The composition preferably comprises from 3 to 10 parts of dye of Formula (1) to 1 part of one or more dyes of Formula (2), preferably 4 to 7 parts of dye of Formula (1 ) to 1 part of one or more dyes of Formula (2), more preferably 5 to 6 parts of dye of Formula (1 ) to 1 part of one or more dyes of Formula (2), especially 5 parts of dye of Formula (1 ) to 1 part of one or more dyes of Formula (2); wherein the parts are by weight.

In compositions of the invention, an especially preferred magenta dye of Formula (2) is of the Formula (8) or a salt thereof:

Formula (8)

Dyes of Formula (1) can be prepared according to standard synthetic methods commonly used in the dyestuff art, involving sequential diazotisation of amines (typically using NaNO₂ in dilute mineral acid at < 5°C) and coupling the resultant amines onto the desired coupling components. These commonly used methods are described in detail in DT-2254835-C3, column 6, line 1 to the end of column 38, which are herein incorporated by reference thereto.

Dyes of Formula (2) can be prepared according to standard synthetic methods such as those described in EP-B-679173, pages 3, line 52 to page 4, line 14, which are herein incorporated by reference thereto.

The dyes of Formula (1 ) and (2) may be converted into the free acid form or into a salt with a counter ion other than sodium by using well known techniques. For example, the alkali metal salts of the dye of Formula (1 ) and (2) may be converted into a salt with ammonia or an amine by dissolving the dye in the form of a salt with an alkali metal, acidifying with a mineral acid and adjusting the pH of the solution to pH 9 to 9.5 with ammonia or the amine and removing the alkali metal cations by dialysis. An example of a suitable process for converting the sodium salt of the dye of Formula (1) or (2) to the ammonium salt is analogous to that described in Example 21 of EP0356080A.

The compositions according to the present invention are particularly useful when incorporated into inks for use in ink jet printers because they provide high quality prints with a good optical density, good fastness properties and a particularly desirable neutral black shade. These effects are achieved even on inexpensive plain paper.

The dyes present in the compositions according to the present invention may be in free acid form but are preferably in the form of water-soluble salt. Preferred salts are alkali metal salts, especially lithium, sodium and potassium salts or ammonium and substituted ammonium salts. Especially preferred salts are those formed with ammonia and volatile amines.

The dyes in the compositions according to the present invention may be, and preferably are, purified to remove undesirable impurities before they are incorporated into inks for ink jet printing. Preferably the total concentration of undesirable ions is less than 10 parts per million, more preferably less than 5 parts per million, by weight relative to the weight of ink. Conventional techniques may be employed for purifying the dyes, for example ultrafiltration, reverse osmosis and/or dialysis.

According to a second aspect of the present invention there is provided an ink comprising:

(i) 0.01 to 20 parts of a composition according to the first aspect of the present invention; and (ii) 99.99 to 80 parts a liquid medium or a low melting point solid medium; wherein all parts are by weight and the number of parts (i) + (ii) = 100. The number of parts of component (i) is preferably from 0.1 to 15, more preferably 1 to 10 and especially from 2 to 8.

It is preferred that when the medium is liquid, that the components present in the composition according to the first or second aspect of the present invention are dissolved completely in the medium to form a solution. Preferably the compositions have a solubility of 10% or more in the medium because this allows the preparation of concentrates which may be used to prepare more dilute inks and to minimise the chance of precipitation of colorant if evaporation of the liquid medium occurs during storage of the ink.

When the medium is a liquid it preferably comprises water, a mixture of water and one or more organic solvent(s), or an organic solvent. When the medium comprises a mixture of water and one or more organic solvent(s), the weight ratio of water to organic solvent(s) is preferably from 99:1 to 1 :99, more preferably from 99:1 to 50:50 and especially from 95:5 to 70:30.

It is preferred that the organic solvent(s) present in the mixture of water and organic solvent(s) are water-soluble organic solvent(s). Preferred water-soluble organic solvent(s) are selected from C^-alkanols, for example methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, isobutanol and n-pentanol; cyclic alkanols, for example cyclohexanol and cyclopentanol; diols, preferably diols with 2 to 12 carbon atoms, for example pentane-1 ,5-diol; amides, for example dimethylformamide or dimethylacetamide; ketones or ketone-alcohols, for example acetone, methyl ether ketone, cyclohexanone and diacetone alcohol; ethers, for example tetrahydrofuran or dioxane; oligo- or poly-alkylene- glycols, for example diethylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol and polypropylene glycol; alkyleneglycols or thioglycols containing a C_2-6-alkylene group, for example ethylene glycol, propylene glycol, butylene glycol, pentylene glycol hexylene glycol and thiodiglycol; polyols, for example glycerol, pentan-1 ,5-diol and 1 ,2,6-hexanetriol; C^-alkyl-ethers of polyhydric alcohols, for example 2-methoxyethanol,

2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy)ethoxy]- ethanol, 2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol, 2-(2-butoxyethoxy)ethanol and ethylene- glycol-monoallylether; cyclic amides, for example 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and 1 ,3-dimethylimidazolidone; cyclic esters, for example caprolactone; sulphoxides, for example dimethyl sulphoxide and sulpholane or mixtures containing two or more, especially from 2 to 8, of the aforementioned water- soluble organic solvents, for example thiodiglycol and a second glycol or diethylene glycol and 2-pyrrolidone.

Especially preferred water-soluble organic solvents are 2-pyrrolidone; N-methyl- pyrrolidone; alkylene- and oligo-alkylene-glycols, for example ethyleneglycol, diethyleneglycol, triethyleneglycol; and lower alkyl ethers of polyhydric alcohols, for example 2-methoxy-2-ethoxy-2-ethoxyethanol; and polyethyleneglycols with a molecular weight of up to 500.

A preferred mixture of water and water-soluble organic solvents comprises: (a) from 60 to 80 parts water; and

(b) from 0.5 to 25 parts in total of one or more solvents selected from diethylene glycol 2-pyrrolidone, N-methylpyrrolidone, cyclohexanol, caprolactone, caprolactam,pentane-1 ,5-diol, 2-(2-butoxyethoxy)ethanol and thiodiglycol; ethylene glycol and glycerol; wherein the parts are by weight and the sum of the parts (a) and (b) = 100. Examples of further suitable ink media comprising a mixture of water and one or more organic solvent(s) are given in US 4,963,189, US 4,703,113, US 4,626,284 and EP 4,251, 50A which are incorporated herein by reference thereto.

It is preferred to prepare the inks in a high purity form as is conventional for thermal ink jet printers. A combination of ultra-filtration (UF), reverse osmosis (RO) and ion exchange may be used to render the total concentration of undesirable ions (e.g. halide, nitrite, nitrate, sulphate, peroxide, divalent metal, trivalent metal and silicon) to less than 5 or 10 parts per million by weight relative to the weight of ink.

When the medium comprises an organic solvent it preferably has a boiling point of from 0 to 300°C, more preferably of from 50 to 200°C. The organic solvent may be water-immiscible or water-soluble. Preferred water-soluble organic solvents are any of the hereinbefore mentioned water-soluble organic solvents Preferred water-immiscible solvents include, for example, aliphatic hydrocarbons, esters, such as ethyl acetate, chlorinated hydrocarbons, such as CH₂CI₂ and ethers, such as diethyl ether. When the medium comprises a water-immiscible organic solvent a polar solvent such as an alcohol, ester, ether or amide is preferably added to enhance the solubility of the dyes in the medium. It is especially preferred that where the medium comprises an organic solvent, this is a ketones, especially methyl ethyl ketone or an alkanol especially ethanol and/or and n-propanol. When the medium comprises an organic solvent, it may comprise a single organic solvent or a mixture of two or more organic solvents. It is preferred that the medium comprises a mixture of 2 to 5 different organic solvents because this allows control to be exerted over the characteristics of the ink.

Inks in which the medium is wholly or mainly an organic solvent are used where fast drying times are required and particularly when printing onto hydrophobic and non absorbent substrates such as plastics, metal or glass.

When the medium for the ink comprises a low melting point solid, the melting point of the solid is preferably in the range from 60°C to 125°C. Suitable low melting point solids include long chain fatty acids or alcohols, preferably those with C_18-24 chains and sulphonamides. The composition according to the first aspect of the present invention may be dissolved or finely dispersed in the low melting point solid.

The compositions according to the present invention are particularly useful as colorants for aqueous inks because they have an attractive neutral black shade, exhibit high solubility in water and aqueous media and have high humidity and ozone fastness on substrates, often surface treated papers, used for the preparation of photorealistic prints. Accordingly, it is preferred that the ink medium is water or, more preferably, a mixture of water and one or more water-soluble organic solvent(s).

The medium may contain other components conventionally used in ink jet printing inks, for example viscosity and surface tension modifiers, corrosion inhibitors, kogation reducing additives, and surfactants which may be ionic or non-ionic. According to a third aspect of the present invention, there is provided a process for printing a substrate with an ink using an ink jet printer, characterised in that the ink is as defined for the second aspect of the present invention.

The ink jet printer preferably applies the ink to the substrate in the form of droplets which are ejected through a small orifice onto the substrate. Preferred ink jet printers are piezoelectric ink jet printers and thermal ink jet printers. In thermal ink jet printers, programmed pulses of heat are applied to the ink in a reservoir having a small orifice by means of a resistor adjacent to the orifice, thereby causing the ink to be ejected through the orifice in the form of small droplets directed towards the substrate during relative movement between the substrate and the orifice.

The substrate used in the ink jet printing process is preferably paper, plastic, textile, metal or glass, more preferably paper, an overhead projector slide or a textile material, and especially paper.

Preferred papers are plain or treated papers which may have an acid, alkaline or neutral character.

According to a fourth aspect of the present invention, there is provided a paper, an overhead projector slide or a textile material printed with an ink composition as hereinbefore defined for the second aspect of the present invention, or by means of the process according to the third aspect of the present invention. A fifth feature of the present invention provides an ink jet printer cartridge, optionally refillable, comprising a chamber and an ink wherein the ink is present in the chamber and is an ink according to the second aspect of the present invention.

The invention is illustrated by the following examples.

Examples 1 and 2

Preparation of dye compositions

Dye compositions may be prepared having the following ingredients and amounts shown in Table 1. The amounts quoted refer to the number of parts by weight of each component. Dyes 1 and 2 are the Na⁺ and NH₄ ⁺ salts respectively of the dyes shown below.

Dye 1 can be prepared by standard synthetic methods such as those described in DT-2254835-C3, columns 6 - 38, particularly Example 52, and is also available commercially as Luganil™ Black NT from BASF. Dye 2 can be prepared by standard synthetic methods such as those described in EP-B-679173, particularly Example 3.

The dyes in the compositions may be purified to remove undesirable impurities by conventional techniques such as ultrafiltration, reverse osmosis and/or dialysis, such that the total concentration of undesirable ions is less than 5 parts per million (p. p.m.) relative to the weight of ink. Table 1

Dye 1

Dye 2

Examples 3 and 4 Preparation of inks Inks were prepared having the following composition where all amounts are parts by weight

(a) 3 parts of a dye composition according to one of the above examples

(b) 90 parts water;

(c) 5 parts diethylene glycol; and ( (dd)) 5 5 p paartrtss N-methyl pyrollidone.

The composition used in the ink examples is shown in Table 2.

Table 2

The inks may be purified using standard ultrafiltration(UF), reverse osmosis (RO) and ion exchange techniques to give very low (<5 p.p.m) concentrations of undesirable ions.

Example 5 Ink-jet Printing

The inks described in Examples 3 and 4 were ink-jet printed onto a variety of papers using a Hewlett Packard DeskJet 560C™. The CIE colour co-ordinates of each print (a, b, L, Chroma and hue) were measured using a Xrite 983 Spectrodensitometer™ with 0°/45° measuring geometry with a spectral range of 400-700nm at 20nm spectral intervals, using illuminant C with a 2° (CIE 1931) observer angle and a density operation of status T. No less than 2 measurements were taken diagonally across a solid colour block on the print with a size greater than 10mm x 10mm. The properties of the resultant prints are shown in Table 3.

Table 3

Light Fastness

To evaluate light fastness the prints were irradiated in an Atlas Ci35 Weatherometer™ for 100 hours. The results are shown in Table 4 where degree of fade is expressed as ΔE where a lower figure indicates higher light fastness. ΔE is defined as the overall change in the CIE colour co-ordinates L, a, b of the print and is expressed by the equation ΔE = (ΔL² + Δ a² + Δb^{2 5}. Table 4

Ozone Fastness

The inks from Examples 3 and 4 were printed onto the substrate shown using a Canon 4300™ IJ printer. The printed substrate was then assessed for ozone stability using an ozone test cabinet from Hampden Test Equipment. The test was carried out for two and a half hours at 40°C and 55% relative humidity in the presence of 400 parts per hundred million of ozone. Fastness of the printed ink to ozone was judged by the difference in the optical density before and after exposure to ozone using an Xrite 983™ Spectrodensitometer. Thus, the lower the %OD loss the greater the ozone fastness. Results are shown below in Table 5 and these clearly demonstrate that inks based on compositions of this invention display good ozone fastness.

Table 5

Further Inks

The inks described in Tables I and II may be prepared wherein the Dye Mixture described in the first column is the composition made in the above example of the same number. Numbers quoted in the second column onwards refer to the number of parts of the relevant ingredient and all parts are by weight. The inks may be applied to paper by thermal or piezo ink-jet printing.

The following abbreviations are used in Table I and II:

PG = propylene glycol

DEG = diethylene glycol

NMP = N-methyl pyrollidone

DMK = dimethylketone

I PA = isopropanol

MEOH = methanol

2P = 2-pyrrolidone

MIBK = methylisobutyl ketone

P12 = propane-1 ,2-diol

BDL = butane-2,3-diol

CET= cetyl ammonium bromide

PHO = Na₂HPO₄ and

TBT = tertiary butanol

TDG = thiodiglycol

0

X. to

I-

Claims

1. A composition comprising a black dye of Formula (1) or salt thereof and a magenta dye of Formula (2) or salt thereof:

Formula (1)

wherein: A and B are optionally substituted aryl groups, substituents on A being selected from NO₂ CN, SO₃H, CO₂H and substituents on B being selected from

NR^aR^b where R^a and R^b are each independently selected from H or optionally substituted C_1-6 alkyl; m is 0 or 1 ; n is 0 or 1 ; such that m + n is not less than 1 ;

Z is

R¹ and R² are each independently chosen from H or optionally substituted alkyl, optionally substituted alkoxy, SO₃H or CO₂H; is chosen from NH, SO₂NH and CONH;

Ar¹-N=N-J-X-G-X-J-N=N-Ar²

Formula (2)

wherein:

Ar¹ and Ar² are each independently aryl each of which carries at least two carboxy groups; and each J is independently

G is a group of the Formula (3a) or (3b):

a b Formula (3) in which

T¹ and T² are each independently H, C_1-4-alkyl, C_1-4-alkoxy or C₃.₄-alkenyl; and T³ and T⁴ are each independently H, C_1-4-alkyl, C_1-4-alkoxy or C_3-4-alkenyl provided that T³ and T⁴ are not both H; each X independently is a group of the Formula (4), (5) or (6):

5

Formulae (4) - (6)

2. A composition according to claim 1 wherein the black dye of Formula (1 ) is of the Formula (7) shown below or a salt thereof:

Formula (7)

3. A composition according to either of the previous claims wherein the magenta dye of Formula (2) is of the Formula (8) shown below or a salt thereof:

4. A composition according to any one of the previous claims comprising from 3 to 10 parts of dye of Formula (1 ) to 1 part of one or more dyes of Formula (2).

5. An ink comprising:

(i) 0.01 to 20 parts of a composition according to any one of claims 1 to 4; and (ii) 99.99 to 80 parts a liquid medium or a low melting point solid medium; wherein all parts are by weight and the number of parts (i) + (ii) = 100.

6. An ink according to claim 5 wherein the total concentration of undesirable ions is less than 10 parts per million by weight relative to the weight of ink.

7. A process for printing a substrate with an ink using an ink jet printer, characterised in that the ink is as defined in claim 5 or 6.

8. A paper, an overhead projector slide or a textile material printed with an ink composition as defined in claim 5 or 6 or by means of the process according to claim 7.

9. An ink jet printer cartridge, optionally refillable, comprising a chamber and an ink according to claim 5 or 6 wherein the ink is present in the chamber.

10. An ink or a composition substantially as described in any one of the Examples herein.